When I downvote posts I get "Please consider adding a comment if you think this post can be improved." popping up in an overlay. That's fine as a "once in a while" reminder, but it's shown every time, which gets rather annoying when downvoting several posts in a row. Similarly, the "remember you can mark this answer as accepted" message can get annoying when I'm usually just about to do that or I'm upvoting multiple answers, but can only accept one of them.

I have two suggestions:

Adding some limits one how often these are shown. I don't think either warning should be shown more than once every few hours. Alternatively, you could avoid showing it more than once per thread (or perhaps per thread per day).

A user option to turn this feature off entirely. I'm well aware of my ability to comment and accept answers. It's just not something I need to be reminded of all the time.

OK, that explains why I still get the message. So it's not a bug, it's a feature. :) But I still think the feature is an unnecessarily annoying one.
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EMPDec 15 '09 at 22:16

It's annoying only if it's unnecessary, but unfortunately the SO engine is unable to determine if it's necessary :) Perhaps it could make a better attempt, say to only show the popup for the first N downvotes a user gives, but that's a harder calculation as it requires a DB search.
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EtherDec 15 '09 at 22:22

I’m 100% with Evgeny here. You are annoying your users, not encouraging them, by telling them they have to work and sweat for months before they can have any reasonable non-annoying behaviour from a website.
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TimwiAug 22 '10 at 14:08